With the remarkable advances in the fields of solid-state imaging devices and various hard-copy printing technologies made in recent years, the comparison between electronic imaging systems and the silver-halide photographic system has become a frequent subject of discussion. Nevertheless, the superiority of the silver halide photographic system with respect to high sensitivity and high image quality, particularly with respect to affordable consumer products, will not be threatened for some time in the future. One particular shortcoming of the silver-halide system, however, in comparison to electronic imaging systems is that the photographic element requires a so-called wet-development process that typically requires substantial volumes of solutions such as developing, fixing, and bleaching solutions. For the people engaged in the development of silver-halide photographic techniques, the development of a "dry" or "apparently dry" development process for the silver-halide color photographic system has been a goal for many years. By "apparently dry" is meant that a small or minimal amount of water or alkaline water may be added to a film to develop it, but that the conventional series of tanks, including complex chemicals, may be avoided.
A dry or apparently dry development process can be accomplished by the use of photothermographic elements described in Research Disclosure 17029 (Research Disclosure I). Generally, in these kinds of systems, development occurs by reduction of silver ions in the photosensitive silver halide to metallic silver as in conventional non-thermal systems, but the developing agent is contained within the element, so that it is unnecessary to immerse the photographic element in an aqueous solution containing a developing agent. Various types of photothermographic elements have been proposed and patented. Research Disclosure I discloses a type A and a B photothermographic system. Type A elements contain in reactive association a photosensitive silver halide, a reducing agent or developing agent, an activator, and a coating vehicle or binder. A problem has been to achieve a commercially viable system that produces a quality of image comparable, in the eyes of the average film consumer, to traditional silver-halide film.
A practical color photothermographic system for general use with respect to consumer cameras would have significant advantages. Such film might be amenable to development at kiosks, with the use of simple dry or apparently dry equipment. Thus, it is envisioned that a consumer could bring an imagewise exposed photothermographic film, for development and printing, to a kiosk located at any one of a number of diverse locations, optionally independent from a wet-development lab, where the film could be developed and printed without any manipulation by third-party technicians. It is also envisioned that a consumer might be more prone to owning and operating such film development equipment in a home, particularly if it was dry or apparently dry and did not involve the use of complex chemicals. Thus, the development of a successful photothermographic system could open up new opportunities for greater convenience and speed of development, even immediate development in the home for a wider cross-section of consumers.
In order to maintain the dry or apparently dry aspect of a photothermographic system, various possibilities exist. One, for example, is to fix/bleach (remove the silver and silver halide) in effect by a diffusion transfer. See, for example EP 0762 201 to Matsumoto et al assigned to Fuji Photo Film Co. With the advance of scanning technologies, it has now become natural and practical for photothermographic color film to be scanned, which can be accomplished without the necessity of removing the silver or silver-halide from the negative, although special arrangements for such scanning can be made to improve its quality. See, for example, Simmons U.S. Pat. No. 5,391,443.
It would be desirable if a photothermographic system could be made backwards compatible for use with a conventional wet-development process. Applicants have found that known photothermographic systems are not adaptable or readily adaptable for backwards compatibility. Applicants have found serious obstacles to obtaining a photothermographic system that is backwards compatible. For example, type B photothermographic systems, in which an organic silver salt plays the role of a silver ion source but does not function as the photosensor and memory, was not found not to be readily backwards compatible because of the antifoggants typically contained in such film. Photothermographic systems in which the developing agent is unblocked have also presented problems for backwards compatibility. For example, certain unblocked developing agents in the form of metal salt were found to prevent proper hardening of the silver-halide emulsion during manufacture.
Japanese kokai patent publication 10-78638 (Mar. 24, 1998) claims the use of a color photographic element that is backwards compatible by means of using a special combination of two yellow dye couplers with an unblocked ballasted sulfonamidophenol or sulfonyl hydrazide type developing agent. The pair of yellow dye couplers consist of one having a detachable cationic group and one having a detachable anionic group, the latter coupler preferably also containing a dye suppressant. It was found that, in the absence of one of the couplers, the color sensitivity during conventional wet-development was relatively poor, and that in the absence of the other of the two couplers, the granularity during conventional wet-development was relatively poor. As mentioned above, the photothermographic developing agent in Japanese kokai patent publication 10-78638 to Matsumoto et al was unblocked, and this fact may have adversely affected wet-development processing with conventional combinations of couplers and developing agents.
Another disadvantage of the ballasted sulfonamidophenol developing agents or ballasted sulfonylhydrazide developing agents in kokai 10-78638 is that they generally react with couplers to form dyes of low extinction or to form dyes which differ in hue from those formed with phenylenediamine color developing agents, resulting in unwanted color variations. This fact also limits the ability of the developed color negative image, after scanning, to provide visually editable and previewable images.
Blocked developing agents have been disclosed not only for use in photothermographic systems, but for use in non-thermal systems in which they may supplement an externally supplied developing agent. It is known that such developing agents can be introduced into a silver-halide emulsion in blocked form so that deleterious desensitization or fog effects that might otherwise occur due to the presence of such compounds in the film are eliminated. Such developing agents can be made to unblock under conditions of development so that the developing agent is free to participate in image-forming (dye or silver metal forming) reactions.
In these cases, the presence of blocked developing agents may be for providing development in one or more color records of the element, supplementary to the development provided by the developing agent in the processing solution to give improved signal in a shorter time of development or with lowered laydowns of photographic materials, or to give balanced development in all color records.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base precursors of developing agents. Schleigh and Faul, in a Research Disclosure 9129 (1975) pp. 27-30), describes the acetamido blocking of p-phenylenediamines. Subsequently, U.S. Pat. No. 4,157,915, to Hamaoka et al and U.S. Pat. No. 4, 060,418, to Waxman and Mourning describe the preparation and use of carbamate blocked p-phenylenediamines in an image receiving sheet for color diffusion transfer.
Compounds having ".beta.-ketoester" type blocking groups (strictly, .beta.-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the .beta.-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developing agents in film systems in a form from which they only become active when required for development. The .beta.-ketoacyl blocked developing agents are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
The incorporation of these blocked developing agents in photographic elements is typically carried out using colloidal gelatin dispersions of the blocked developing agents. These dispersions are prepared using means well known in the art, wherein the developing-agent precursor is dissolved in a high vapor pressure organic solvent (for example, ethyl acetate), along with, in some cases, a low vapor pressure organic solvent (such as dibutylphthalate), and then emulsified with an aqueous surfactant and gelatin solution. After emulsification, usually done with a colloid mill, the high vapor pressure organic solvent is removed by evaporation or by washing, as is well known in the art.
In order to be acceptable for commercial application, it is necessary that a blocked developing agent be stable before exposure, to avoid desensitizing the silver halide during storage, resulting in increased fog and/or decreased Dmax after development. At the same time, the blocked developing agent must be capable of sufficiently fast unblocking kinetics when the exposed film is being developed. In the case of the same photothermographic film designed for alternatively (at the discretion of the consumer) traditional wet-processing or apparently-dry thermal processing, it is surmised that another requirement might be that the blocked developing agent and/or its associated components not adversely affect or interfere with obtaining the results otherwise achieved by traditional wet-processing.